Hey guys, Im doing the a4 to m6 swap and I got a used flywheel from a 95 Transam lt1 with my kit. I have a 95 z. I was wondering If I want to reuse this flywheel, if I will have to get it balanced or just resurfaced. Also where can I get my flywheel resurfaced? Do autopart stores do it? Thanks guys

 

If you have a stock rotating assy. the balance should be fine. The M6 flywheel and the A4 flexplate have the same balance.

Rich Krause

 

Thanks a million for the info

 

So, all along I've been mistaken in assuming that I would need to balance my new M6 flywheel to match the the A4 flywheel?

Im sure I read about people doing this. What was all that talk I read about doing this? Did I misunderstand something?

Just trying to clarify and understand here, Mr. Krause. Sure would appreciate if you could fill me in.

BTW, if it is in fact the case that flywheels are balanced the same for all LT1's does that then also mean that GM knows that there engines are all out of balance in the same way?

I'm so confused.

 

Yep, that's how it is. Think about it for a minute. The motors for the M6 and A4 are identical. Do you think they balance each one individually. Nope, they are all (nearly) identical and can be balanced with the same amount of weight. So the M6 flywheel and the A4 flexplate are interchangable.

If you want to have any balancing done, the whole assy. can be internally balanced. Problem is, it's expensive. Mallory metal is around $60 per slug and it can take a few pieces to balance a motor. That and some skilled labor. My new rotating assy. cost over $400 to balance internally (4 pieces of Mallory, 3 hours labor). Yes, it's better than a factory balance, but overkill for 99.9% of us.

So, as long as the rotating assy. is stock, you can use a standard counterweighted flywheel/flexplate.

One other thing, the harmonic balancer is neutral balanced and it also interchagable. Also, if you have a new motor internally balanced you can just remove the counterweight from a stock balanced flywheel/flesplate and re-use it.

Rich Krause

 

So why in heaven's name would GM build all their engines with the same "off balance?" You are saying that all LT1 engines are out of balance and they are all off balance by roughly the same amount, correct? That just seems dumb as he%^ to me, from a manufacturing standpoint. If you know they are off fix it at the design stage. Wouldn't that make more sense?

Rich, can you explain what all the talk was about having your new FW balance matched to your old flywheel? I'm sure I read that somewhere and not just once but repeatedly.

Still

 

I am no expert at engine balancing, in theory and practice. But here is how I understand it. Small block Chevys prior to the 400 were balanced internally. Each assembly was not individually balanced, but the crank counterweights were designed to balance the particular piston and rod combo used in each type of motor. The flywheel/flexpate and the stuff on the front of the crank were neutrally balanced.

The LT1 (and the LS1) would require Mallory metal to fully balance internally, so they rely partially on external balance. As I noted earlier, the "bob weights" are the same on each indivivual motor, because the same pistons, wrist pins, connecting rods, and rings are used. I am not sure if GM attempts to weight match pistons and rods, the production tolerance may be close enough that that is not needed. Anyway, the idea is that all of the motors will be close enough that the same external balance weight will be close enough to correct so that the balance is acceptable. The individual motors are not balanced, GM relies on all of the parts having the same weight (more or less).

Small block Fords (289, 302, 351) are also externally balanced but BBC's and Fords are internally balanced. As I understand it, there is less torsional stress on the crank when a motor is completely internally balanced. You can either buy a rotating assy. which is designed to be in balance without drilling the counter weights or adding Mallory metal, or if you mix-n-match parts then either adding or subtracting weight from the counterweights will be needed to balance the motor.

OTOH, if you have a stock rotating assy. and replace parts there are two choices. If OEM parts or equivalent are used you can simply reuse the sotck type flywheel/flexplate. The balance should be as good as it was from the factory in the first place. If you are replacing the flywheel/flexplate, there is no reason to have the new balanced to the old in this situation. If you bought the right replacement partd in the first place, they will balance the same anyway. If you had a custom rotating assy. and it was originally externally balanced, and you replaced parts with identical pieces, you could either use your original f/f or get a new one. In this case, you would need to have the new f/f balanced to match the old one. Or, you could have the new f/f balanced specifically to the new parts. But they should be nearly the same in any case.

If you want a more precise balance, or are using non-stock parts you will need to have it balanced. The new balancing can be internal, external, or both. A fully internally balanced rotating assy. by definition needs a neutral balance f/f.

Hope I didn't muck this explanation up too much.

Rich Krause

 

Excellent explanation Rich! Thankyou very much! I vote you as an expert, for what ever that's worth.

 

I accept the nomination, thanks

Rich Krause